No, they do not have bands of crystals but they are all crystalline.
The size of the crystals in an igneous rock tells us how fast the magma cooled.
Extrusive igneous rock consists of mineral crystals that are not observable with the naked eye. Obsidian is an extrusive igneous rock (volcanic glass) where there technically are no mineral crystals.
If you're not looking for anything specific, any extrusive igneous rock will have smaller crystals, if any at all. This is because they cool quickly on the surface, leaving little time for crystals to form/grow.
Igneous rocks with big crystals or grains form from slow cooling beneath the Earth's surface, allowing time for larger crystals to grow. In contrast, igneous rocks with small crystals or grains form from fast cooling at or near the Earth's surface, limiting the time available for crystal growth.
Granite is a common type of igneous rock that forms visible crystals. It is composed primarily of quartz, feldspar, and mica minerals, giving it a speckled appearance. Granite is often used in construction and countertops due to its durability and visual appeal.
It depends on the cooling rate of the magma. If the magma cools slowly underground, large crystals can form, creating intrusive igneous rocks. If the magma cools rapidly on the Earth's surface, small crystals or glassy textures can result in extrusive igneous rocks.
Igneous rocks can have both small and large crystals, depending on how quickly they cool. If an igneous rock cools slowly beneath the Earth's surface, it can form large crystals, while rapid cooling at the Earth's surface or in an eruption can result in small or no visible crystals.
Granite with larger crystals, basalt with smaller crystals.
Not all of them. Volcanic glass does not have crystals.
The size of the crystals in an igneous rock tells us how fast the magma cooled.
Igneous rocks will develop large crystals is they cool slowly underground.
The size of crystals in an igneous rock is called texture. Texture can range from fine-grained (small crystals) to coarse-grained (large crystals).
Intrusive rock normally has visible crystals. Extrusive igneous rock has small crystals. A black extrusive igneous rock with small crystals could be basalt.
Igneous rocks will develop large crystals is they cool slowly underground.
== Grain size. Most intrusive igneous rocks will have visible crystals. Crystals in most extrusive igneous rocks are not easily visible.
Extrusive igneous rock consists of mineral crystals that are not observable with the naked eye. Obsidian is an extrusive igneous rock (volcanic glass) where there technically are no mineral crystals.
You would expect to find an igneous rock with small crystals near the Earth's surface where the rock cools relatively quickly, such as in volcanic eruptions or magma intrusions that do not have much time to grow large crystals. These rocks are known as volcanic or extrusive igneous rocks.